As opposed to conventional light-emitting apparatuses such as candescent light bulbs and fluorescent light tubes, electron beam-excited light-emitting apparatuses have been recently developed for illumination or image display, using light-emitting phosphors (fluorescent materials) excited by high speed bombardment of electrons released from a field emission electron source in a vacuum vessel. In one of the structures generally used for this new type of apparatus, the light is emitted from a phosphor layer on a glass substrate and transmitted through the glass substrate toward the opposite side from the phosphor layer. In this structure, however, the luminous efficiency is compromised since the light is emitted the most on the electron-irradiated surface of the phosphor layer and wasted within the vacuum vessel.
Accordingly, in order to increase the brightness of the electron beam-excited display apparatuses, there is known a technique for forming a metal back layer by, for example, depositing aluminum on the electron-irradiated surface of the phosphor layer. As described in, for example, Japanese Unexamined Patent Application Publication No. 2000-251797, this metal back layer not only increases the brightness by reflecting the light from the phosphor emitted toward inside of the apparatus to the outer surface (display or illuminating side) of the apparatus with the specular reflection, but also protects the phosphor from damages by applying a predetermined electric potential to the phosphor surface, wherein the damages are caused by the electron charge on the phosphor surface and by the collision of negative ions generated within the apparatus against the phosphor surface.
In order to stabilize the marked quality level of an apparatus for forming and displaying images using light-emitting fluorescent film, the above Japanese Unexamined Patent Application Publication No. 2000-251797 uses a technique for dividing the metal back, disposed on the inner surface of the fluorescent film, into a plurality of portions, and coating the gaps between the portions with a conductive material to prevent creeping discharges on the gap portion surface caused by abnormal electric discharges occurring in vacuum.
However, the technique for using the metal back to improve the luminous efficiency of the apparatus leads to a reduction of the phosphor excitation efficiency due to the acceleration energy loss of the electron beam at the time of its entrance to the metal back layer. Particularly, in an application for an illumination apparatus, this decrease in phosphor excitation efficiency associated with the loss of the electron acceleration energy becomes nonnegligible and hinders the fundamental improvement of the luminous efficiency.
Considering the above situation, the purpose of the present invention is to provide a light-emitting apparatus capable of reducing the wasted excitation light emitted from the phosphor toward inside of the apparatus to thereby improve its luminous efficiency.